Convoluted heat shield

ABSTRACT

A heat shield comprises a convoluted tube preferably formed from two layers of aluminum. The convoluted tube may have an inside minor diameter ranging from 0.5 inches to 3.0 inches and preferably includes convolutions of greater than 0.070 inches and a pitch of at least 0.787 inches. Optionally, the tube is coated with a dark colored or black material to further enhance the heat shielding and dispersing properties. The present invention also includes a method of manufacturing the convoluted tube, and a method of shielding heat from an automobile EGR utilizing an aluminum convoluted tube having convolutions of at least 0.070 inches.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. application Ser. No.60/594,799, filed May 6, 2005, which is hereby incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to reflective convoluted tubing that isused to protect components from radiant heat sources and methods offorming the tubing thereof.

BACKGROUND OF THE INVENTION

There are several different ways in which to insulate a radiant heatsource so that it does not emit heat to effect surrounding components.In many applications, a flexible sleeve is used, as it is easilyinstalled over the heat source-typically an exhaust system, manifold, orexhaust gas recirculation (EGR) system. There are companies worldwidethat manufacture convoluted tubing for many different applications,including insulating a radiant heat source.

Other products that serve a similar purpose are sold by Federal-MogulSystems Protection group under the name Thermflex Spiral. This productis formed from a braided fiberglass tube or sock that is then coatedwith an anti-fray coating and dipped on both ends to help keep theproduct from splitting. A similar product is sold by Vitrica S.A. de C.Vbut uses a different weave pattern in the braided fiberglass tube andcoating to help bond the tube.

The prior art devices discussed above all utilize fiberglass in theconstruction of the heat shield. Some of the disadvantages withfiberglass include the fact that fiberglass is relatively expensive, andfiberglass tends to retain heat. The present invention attempts toovercome one or more problems associated with the prior art heat shielddevices. Accordingly, the present invention is hereby submitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a convoluted tube in accordance with apreferred embodiment of the present invention.

FIG. 2 is an end view of a convoluted tube of FIG. 1.

FIG. 3 is a side view of a worm inner die member.

FIG. 4 is an end view of the worm die member of FIG. 3.

FIG. 5 is an end view of an outer nut die member.

FIG. 6 is a cross-sectional view of the nut die member of FIG. 5.

FIG. 7 is a cross-sectional view of a convoluted tube.

FIG. 8 is a side view of a convoluted tube, illustrated with end cap.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

One embodiment of the present invention provides a flexible convolutedtube 10 made from layers of material that are wrapped on a mandrel, andthen pass though a set of dies 20, 30 to convolute the material. Oncethe material is convoluted, it then passes through a heat zone thatthermally sets a layer of adhesive that is previously applied to one ofthe material layers.

At present, the standard product manufactured on this equipment toproduce a heat insulator has included using thin woven fiberglassblanketing that is placed on the inside of the convoluted tubing, andapplying a layer of stainless steel to the outside, or placing thefiberglass between two layers of aluminum.

One limitation to the standard die design and resulting finishedconvoluted tube is that there is a limited amount of material on thedies to manufacture a deeper groove to produce a taller thread, which inturn produces a taller or bigger wall thickness of the convoluted tube.In the traditional process of manufacturing the die threads, the leadingedge of one thread will cut or erode into the trailing edge of the nextthread, which will limit the total thread height of the die.Additionally, if the threads are too tall on a die, the current designwill not allow for the material to flow through the dies and will causethe material to either be cut or perforated once leaving the die, or thematerial will not pass through the die at all.

Through testing of various material combinations, it was determined thatif merely two layers of aluminum were utilized without a layer offiberglass, the resultant combination worked as well as or better than aproduct that includes fiberglass. As such, in one embodiment of thepresent invention may comprise a convoluted tube 10 consisting of twolayers of aluminum and convolutions 12. The thermal conductiveproperties of aluminum are superior to that of fiberglass in someapplications. Fiberglass acts as an insulator/absorber of heat, whilealuminum tends to dissipate heat. The significance of removing thefiberglass is that the final product costs less, allows for betterdissipation of heat, and does not use a material that causes health andsafety issues when being formed or installed.

To further improve the performance of this new product, experimentationwas done to the design of the winder dies that actually form thefinished product. The die design may include a worm die member 20 thatcomprises a shaft 24 and threads 22. As illustrated in FIGS. 3-6, for astandard die design typically uses a thread height of 0.047″ to 0.055″ ,the difference of the Major Outside Diameter (OD) and the Minor InsideDiameter (ID) divided by two of either the worm or nut die, for tubesizes ranging from 0.50″ to 3.00″ diameter. Also, the standard pitch is0.394″ to 0.787,″ the pitch being the longitudinal distance that ittakes one thread to make a full circumference of the die. Additionally,this die design uses a multi-lead thread, ranging from 4 to 6 leads,increasing the design complexity. A standard Acme Thread design usesonly one lead.

The nut die member 30 comprises an aperture that receives the worm diemember 20. The perimeter of the aperture may comprise threads 32. Viathe cooperation between threads 22 on worm die member and threads 32 onnut die member, the tube is convoluted as it passes between the two diemembers 20, 30.

An exemplary embodiment of an improved die design 20, 30, uses a rangeof 0.063″ to 0.079″ for the thread height for the same size range ofdies, and increases the pitch to 0.787″ to 1.38.″ This is roughly a 33%to 43% increase in the thread height, and a 100% increase in pitch for a0.5 inch tube and a 75% increase for a 3.0 inch tube from the standarddesign. The end result creates a taller distance between the peaks andvalleys of the convoluted tube. If we assume a 0.75″ IDAluminum-Fiberglass-Aluminum tube that is currently sold today has atotal material thickness of 0.013″ and a wall height of 0.067″, then youcan extrapolate the straight part of the convolution to be approximatelythe wall height less two times the thickness or 0.067-(2*0.013)=0.041.″

The following table provides an exemplary configuration for differentsized tubes according to an exemplary embodiment of the presentinvention, compared to prior art tubes. Prior Art Exemplary EmbodimentsTube Thread Convolution Thread Convolution ID Height Pitch Height HeightPitch Height 0.492 0.047 0.394 0.059 0.063 0.787 0.071 0.787 0.055 0.7870.067 0.079 1.181 0.094 1.024 0.055 0.787 0.071 0.079 1.181 0.098 1.9690.055 0.787 0.071 0.079 1.181 0.110 2.992 0.055 0.787 0.079 0.079 1.3780.118

An embodiment of the present invention provides a 0.75″ IDAluminum-Aluminum tube, FIG. 5, that has a total material thickness of0.005,″ and a convolution height CH of 0.079″ or greater. Thistranslates to a straight part of the convolutions of approximately0.069.″ This is roughly a 67% increase in the straight section of theconvolution, and a 67% increase in the surface area where the greatestamount thermal conductivity occurs. A convolution height ranging to atleast 0.118″ is also contemplated.

Additionally, it has been found that by coating the exterior surface ofthe new tubing design with a dark color or black outer surface furtherenhances the heat dissipation properties of the convoluted tubing. Forexample, the tubing may comprise a black epoxy coating, which may bebaked-on or air-dried. Alternatively, the outer surface may be anodized,powder coated, or painted, or may have any of a plurality of dark orblack coatings as are known in the art.

Optionally, an end cap 16 may be added to one or more ends of the tubeto provide a smoother end surface and to help in preventing the ends ofthe tube from fraying or coming apart. It is contemplated that the endcaps may be attached to the tube via any means as are known in the artwithout deviating from the scope of the present invention.

This new design has allowed for a lower cost product that performsbetter and is easy to install as it is more flexible, and removes anyadditional worker health and safety issues. This design also allows forthe potential to use other thicknesses of material to increase ordecrease the flexibility of the end product without sacrificing cost orperformance.

1. A heat shield, comprising: an elongated convoluted tubing having aplurality of convolutions, the elongated tubing consisting essentiallyof a first layer of aluminum and a second layer of aluminum.
 2. The heatshield as recited in claim 1, wherein, the convolutions comprise aheight equal to a difference between a major outside diameter of theheat shield and a minor inside diameter of the heat shield, the heightof the convolutions is at least 0.070 inches; and, the minor insidediameter is approximately 0.50 inches.
 3. The heat shield as recited inclaim 2, wherein the pitch of the convolutions is at least 0.787 inches.4. The heat shield as recited in claim 1, wherein, the convolutionscomprise a height equal to a difference between a major outside diameterof the heat shield and a minor inside diameter of the heat shield, theheight of the convolutions is at least 0.090 inches; and, the minorinside diameter is between 0.75 inches and 3.0 inches.
 5. The beatshield as recited in claim 4, wherein a pitch of the convolutions is atleast 0.118 inches.
 6. The heat shield as recited in claim 4, whereinthe minor inside diameter is about 0.75 inches, and the convolutionheight is about 0.094 inches.
 7. The heat shield as recited in claim 6,wherein a pitch of the convolutions is at least about 1.18 inches. 8.The heat shield as recited in claim 4, wherein the minor inside diameteris about 1.0 inches and the convolution height is about 0.098 inches. 9.The heat shield as recited in claim 8, wherein a pitch of theconvolutions is at least about 1.18 inches.
 10. The heat shield asrecited in claim 4, wherein the minor inside diameter is about 2.0inches and the convolution height is about 0.110 inches.
 11. The heatshield as recited in claim 10, wherein a pitch of the convolutions is atleast about 1.18 inches.
 12. The heat shield as recited in claim 4,wherein the minor inside diameter is about 3.0 inches and theconvolution height is about 0.118 inches.
 13. The heat shield as recitedin claim 12, wherein a pitch of the convolutions is at least about 1.37inches.
 14. The heat shield as recited in claim 4, wherein the heatshield further consists of a black outer coating.
 15. The heat shield asrecited in claim 4, further comprising an end cap attached to at leastone end of the tubing.
 16. A method of shielding heat generated from anautomobile exhaust gas recirculation system (EGR), the EGR having aconduit for diverting exhaust gas, the method comprising: at leastpartially surrounding the conduit with a convoluted tube, wherein theconvoluted tube consists essentially of two layers of aluminum, theconvoluted tube including convolutions comprising a height equal to adifference between a major outside diameter of the convoluted tube and aminor inside diameter of the convoluted tube, wherein, the height of theconvolutions is at least 0.090 inches; and, the minor inside diameter isbetween about 0.75 inches and about 3.0 inches.
 17. The method asrecited in claim 16, wherein the pitch of the convolutions are at leastabout 1.18 inches.
 18. The method as recited in claim 17, wherein thetube further comprises a dark-colored coating.
 19. A method of forming aconvoluted tube, comprising: wrapping layers of aluminum around amandrel having a diameter of 0.5 inches to 3.0 inches, wherein at leastone of the layers includes an adhesive; passing the wrapped layersbetween a worm and nut die to convolute the material, wherein the wormand the nut each have a thread height of at least 0.063 inches and apitch of at least 0.787 inches; and, passing the convoluted layersthrough a heat zone to thermally set the adhesive and substantially bondthe layers together.
 20. The method as recited in claim 19, wherein thediameter of the convoluted tube is between 0.75 inches and 3.0 inches,the thread height is at least 0.075 inches, and the pitch is at leastabout 1.18 inches.